Secondary batteries are so-called rechargeable batteries, widely used in many products, such as notebooks, tablets, mobile phones, and even large electric vehicles and robots. Although a rechargeable battery is composed of a number of rechargeable battery cells linked in series or parallel, according to different power supply targets, there are different specifications of output current and voltage.
Since each cell has its unique characteristics when the secondary battery is assembled, it leads to an unbalance problem for the cells of the secondary battery in use no matter it is charging or discharging. Abnormal operations will cause the temperature of the secondary battery to be high, reduce life time of the battery, and even make the battery explode. Reduced life time of the secondary battery mainly suffer from overcharging or over-discharging operations. Therefore, general secondary batteries will have a battery management chip to settle the problems above.
Please see FIG. 1. A structure of a conventional secondary battery 1 is shown. There is a battery management chip 2. A source for storing and providing power for the secondary battery 1 are several cells 3 linked to each other in series. The battery management chip 2 is linked to the group of the cells 3 and can detect the status of each cell 3 effectively. Dynamic balance of the cells 3 is available. In addition, the battery management chip 2, the charging control switch 4 and the discharging control switch 5 from a protective circuit for charging and discharging. The charging control switch 4 and the discharging control switch 5 are composed of a field effect transistor and a parasitic diode. The protective circuit further connected to a terminal unit 6. The terminal unit 6 has a positive terminal 6a, a negative terminal 6b and a data transmission terminal 6c. The terminal unit 6 may be in the form of a plug. Depending on the target linked, the secondary battery 1 can decide to charge or discharge. The battery management chip 2 can send the status of the cells 3 to an external control system outside the secondary battery 1 through the data transmission terminal 6c. The battery management chip 2 can also receive instructions from the control system via the data transmission terminal 6c to manage the cells 3.
When the target which the terminal unit 6 is linked to is a charger, the current goes from the positive terminal 6a, to the cells 3, the discharging control switch 5 and the charging control switch 4, sequentially. Last, is passes the negative terminal 6b and returns back to the charger. Now, the charging control switch 4 and the discharging control switch 5 stay turned on. The battery management chip 2 knows the direction of the current by the resistor 7, further being aware of the status of charging. When the target which the terminal unit 6 is linked to is a load, the current flows from the cells 3, to the positive terminal 6a and the load. The load also has current flows to the negative terminal 6b, the charging control switch 4 and the discharging control switch 5, going back to the cells 3. The loop completes. At this moment, the charging control switch 4 and the discharging control switch 5 also in the status of turned on. The battery management chip 2 knows it is discharging depending on the direction of current through the resistor 7.
When the secondary battery 1 is charged, if an over-charged situation comes out (namely, the voltage of the secondary battery 1 is over its maximum rating voltage when in charging), the battery management chip 2 will turn off the charging control switch 4 to protect the secondary battery 1 from damage due to keeping charging. Similarly, when the secondary battery 1 discharges, if an over-discharged situation comes out (namely, the voltage of the secondary battery 1 is lower than a minimum allowable voltage value when discharging), the battery management chip 2 turns off the discharging control switch 5 to protect the secondary battery 1 from losing its rechargeability due to keeping discharging. When the over-charged protection is going on, since the voltage of the secondary battery 1 drops with time, as it is lower than the maximum rating voltage, the battery management chip 2 can work again to turn on the charging control switch 4, thus, the secondary battery 1 can also function well. However, when the over-discharged protection is going on, since the voltage of the secondary battery 1 is not able to come back to the normal operating voltage, unless a compulsory action takes place out of the battery for recovery, the secondary battery 1 can not function normally.
For end users, if the secondary battery is protected due to over-discharge and cannot come back to normal operations, they must think the secondary battery is damaged. The vendor of the secondary battery is asked for exchange. Even the vendor is willing to exchange a good secondary battery for with the original one, the cost for transportation is a lost to the vendor. Therefore, a design for relative circuit to effectively reboot the secondary battery for normal operations after the secondary battery is protected for being over discharged is desired.